An image forming apparatus includes a pulse motor in order to rotate sections that need to rotate (e.g., a photoconductive drum and a sheet conveying roller). The pulse motor is driven by a motor driving current supplied from a motor driving control device and rotates a predetermined amount according to a pulse train supplied from the motor driving control device.
The motor driving control device supplies the motor driving current to the pulse motor such that the pulse motor supplies torque larger than step-out torque (torque at least necessary for rotating a load) to a load (e.g., the sheet conveying roller).
For example, the load of the sheet conveying roller fluctuates according to temperature in the image forming apparatus and increases as the temperature of the inside of the image forming apparatus is lower.
In the image forming apparatus in the past, a current value of the motor driving current supplied from the motor driving control device is set such that torque larger than step-out torque during a large load and low temperature (e.g., −5° C.) is supplied to the load. Since the current value of the motor driving current is set in this way, even if load fluctuation occurs because of fluctuation in temperature, the pulse motor supplies torque larger than step-out torque during the load fluctuation to the load. Therefore, it is possible to suppress the pulse motor from stepping out.
However, even if a load is small, for example, even if the temperature of the image forming apparatus is the room temperature (e.g., 20° C.), the motor driving control device supplies a motor driving current having a current value set with reference to a large load to the pulse motor. Therefore, if a load is small, since an electric current more than necessary is supplied to the pulse motor, the image forming apparatus in the past wastefully consumes electric power.
When the electric current more than necessary is supplied to the pulse motor, a heat value of the pulse motor increases. According to heat generation, torque generated by the pulse motor decreases and the pulse motor steps out. Therefore, in the past, it is difficult to continuously drive the pulse motor for a long time. In order to continuously drive the pulse motor for a long time, it is necessary to take measures, for example, adopt a pulse motor that can generate larger torque or provide a cooling mechanism such as a fan or a heat radiation plate for cooling the pulse motor.